Viruses are considered to be among the smallest particles known to man. Viruses are about a hundred times smaller than bacteria, and make up a group of submicroscopic infectious agents that are unable to grow or reproduce outside of a host cell. Certain viruses can cause harm or death in their infected host. Because of their small size, viruses are extremely difficult to detect and characterize. Detection and identification of viruses have been a complicated process in any given environment, especially under combat conditions where pathogenic viruses can be used in biological warfare (BW). Devices are needed which enable detection of remote dispersal of BW agents in a field environment for early warning capabilities.
Rapid detection and warning are essential for providing protection of civilians and soldiers from a BW attack. Previous known methods utilizing biochemical reagents such as multiplex polymerase chain reaction (PCR), low-stringency nucleic acid hybridization and polyclonal antibodies, are often impractical in the field. Polymerase chain reaction is used to detect the presence of a specific genetic sequence, while antibody-based methods detect specific antigens. Both methods work well when testing for known viruses for which genetic primers or antibodies have been developed. Such methods are expensive and typically require time and intensive labor for proper implementation, while providing limited detection capabilities restricted to only certain BW agents.
Biochemical reagent based methods are often hampered by high frequency of false positives under both laboratory and field conditions. The PCR and antibody-based methods require a single test per virus, and often one test per strain of virus. This limits their capacity to monitor and screen all strains of pathogenic viruses in a cost effective manner. Furthermore, these methods cannot actively adapt to rapid mutation of viruses, or emergence of new, unknown viruses, thus failing to provide broad-detection of all viruses regardless of identity, known or unknown, sequenced or un-sequenced.
As set forth in U.S. Pat. Nos. 6,051,189, 6,485,686, 6,491,872, and 7,250,138, assigned to the U.S. Government, viruses may be detected in an environment without reliance on biochemical means by capitalizing on the physical properties of size and density. Suspected viruses can be quickly extracted and detected from an environmental sample through isolation of particles based on sizes and densities, which closely match with those of viral agents. Purification processes can also be used to further concentrate suspected particles to the extent necessary to overcome background contamination. In this manner, reliable and rapid detection of potentially dangerous viruses can be effectively achieved.
This is accomplished through the use of centrifugal techniques, which sorts submicron-sized particles according to density, and differential mobility analysis, which sorts submicron-sized particles according to size. Once isolated and sorted, particles with sizes as small as 2 to 3 nanometers can be detected and counted using a condensation nucleus counter. In this device, a liquid, such as butyl alcohol, is condensed on the particles so they grow to a diameter of about a micrometer. They are then large enough to scatter an appreciable amount of light. By passing these particles through a beam of light, flashes of light are produced. The resulting flashes can be detected and counted to determine the concentration of particles in the flow from the differential mobility analyzer.
In this manner, the resulting particles having a particular density and size matching a particular agent such as viruses are effectively isolated and detected in the sample. The strength of such technology is the capability to detect any virus in a single relatively straightforward test, while providing useful quantitative results. Such systems, however, remain large and bulky and require a substantial amount of time to implement. In addition, the use of condensation nucleus counters often adversely alters the extracted particles in a manner, which render them of limited usefulness for further testing.
Accordingly, there is a need to develop a system and method for sampling and separating submicron-sized particles based on density and/or size to detect the presence of a particular agent such as, for example, viruses in an environmental sample, that is substantially compact, lightweight, cost effective and simple to implement, while enhancing accuracy and reducing false positives. There is a need to develop a system or method for detecting the presence of a particular agent in the environment that enhances constant real-time monitoring with minimal preparation and setup. There is a further need to develop a system and method that does not adversely affect or alter the particular agent upon isolation and detection, in a manner, which hinders further testing or confirmation.